Complete shutdown of the operation of a nuclear reactor, commonly referred to as a scram, is required under any condition wherein continued operation could cause damage to the reactor. A scram is generally effected by releasing vertically disposed "safety" rods carrying neutron-absorbing material at their lower ends, thus allowing the rods to drop to a level wherein they position the absorber material within the reactor core. The inertia of long safety rods limits the speed at which they can be moved to scram position. Furthermore, it is possible that seismic shocks can interfere with the release of absorber carrying rods by bending them so that they cannot slide in their bearings. All scram control mechanisms must, of course, provide a means for returning safety rods to their raised position when an adverse operating condition has been eliminated.
As shown in the description of scram mechanisms presented in the text titled "Fast Reactor Technology: Plant Design", published by M.I.T. Press in 1966, electromagnets have previously been used to hold reactor safety rods in a raised position until an unsafe reactor operating condition occurs, at which time the electromagnets are de-energized to release the rods. An electromagnet is incorporated in some latch mechanisms of embodiments of the invention disclosed herein, but the construction of safety rod release apparatus in accordance with the invention differs from that of known devices. Furthermore, known safety rod release devices use only one release means, whereas in preferred embodiments of this invention a plurality of release latches provide for two types of scram.